CN106699237B - Resource utilization method of straw produced after phytoremediation of soil heavy metal pollution - Google Patents

Abstract

The invention relates to a resource utilization method of straws produced by plants after soil heavy metal pollution remediation. The method comprises the steps of firstly placing crushed straws in a tubular furnace to be calcined into biochar at low temperature, then extracting heavy metals from the biochar containing high-concentration heavy metals in an acidic solution by a liquid phase extraction principle, and separating the heavy metals from the filtered solution by adding an alkaline solution for precipitation reaction. The invention effectively provides a new solution and approach for the subsequent treatment of the heavy metal pollution of the phytoremediation soil, so that the phytoremediation technology is efficiently and continuously developed, and a new approach is provided for the plant resource recovery.

Description

Resource utilization method of straw produced after phytoremediation of soil heavy metal pollution

technical field

The invention relates to a method for recycling and utilizing heavy metals to obtain high-potassium-containing liquid fertilizers by utilizing phytoremediation of heavy metal pollution in soil for the efficient recycling of straws containing heavy metals.

Background technique

For a long time, frequent human activities have caused serious heavy metal pollution to the soil, especially the heavy metal pollution of farmland soil. Heavy metal pollutants cannot be chemically or biologically degraded, easily accumulate in plants, animals and humans through the food chain, and are highly toxic, posing a serious threat to the ecological environment, food safety and human health. For the treatment of heavy metal pollution in soil, the commonly used methods include physical methods such as leaching method, foreign soil method, adsorption and immobilization method, and chemical methods such as biological reduction method and complex leaching method. However, these methods are not only expensive, but most of them can only temporarily alleviate the harm of heavy metals, and may also cause secondary pollution, which cannot fundamentally solve the pollution problem of heavy metals; phytoremediation is environmentally friendly compared to other restoration methods such as chemical and physical Safe and low-cost heavy metal pollution control measures have been applied in the control of heavy metal pollution and site pollution in mining areas. However, some studies have shown that phytoremediation also has some limitations, such as slow restoration speed, and most of the plants that can be used for restoration have no economic value. Tobacco, peanut, oil sunflower, etc. are plants that are easy to absorb and enrich heavy metals, and also contain high concentrations of nutrients such as potassium. The content is still relatively high, and if it is not properly treated, it will lead to secondary pollution. Therefore, the current phytoremediation technology is the current phytoremediation technology. bottleneck.

Common treatment methods for plants mainly include incineration, pyrolysis, ashing, liquid phase extraction, etc. to extract metals. The biggest feature of the above-mentioned disposal technologies is that the restored plants are disposed of as garbage or hazardous waste, rather than comprehensive utilization of these plants.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a resource utilization method of straw produced after phytoremediation of soil heavy metal pollution.

In order to achieve the above purpose, the present invention provides a method for resource utilization of straws produced after phytoremediation of soil heavy metal pollution, comprising the following steps:

1) cleaning and drying the straw after harvesting the mature phytoremediation soil heavy metal pollution;

2) Weigh the dried straw and pulverize it with a pulverizer and place it in a tube furnace fed with high-purity nitrogen for low-temperature firing. L of nitric acid to obtain biochar and ash of metals and other elements. The reason for low temperature firing is that the low melting point of cadmium has less volatilization, and at the same time obtains a higher yield of bio-carbon;

3) After step 2) is completed, put the fired biochar in clean water, adjust its pH to 1-3 with nitric acid, stir for 3 hours, extract heavy metals, and then rinse the biochar with clean water, filter or centrifugal dehydration residual acid in charcoal;

4) Collect the solution extracted in step 3) in a centralized manner, adjust the pH value to 9-11 with potassium hydroxide or potassium carbonate solution, so that the heavy metals are precipitated, and after the heavy metals are recovered by separation and filtration, a high-potassium-containing liquid fertilizer is obtained. The straws after phytoremediation of soil heavy metal pollution in the mature stage are tobacco straws, oil sunflower straws, sesame straws or peanut straws with high potassium content.

In the present invention, the straw produced after the phytoremediation of soil heavy metal pollution in the mature stage is fired into biochar at low temperature in a tube furnace, and then the heavy metals in the biochar are extracted by low-concentration nitric acid, and finally the pH value is adjusted to 9 -11 The heavy metals in the extract are formed and recovered by precipitation. While turning waste into treasure, the heavy metals in the biochar are removed and the heavy metals are recovered. The remaining extract has a high content of nutrient elements and can be used as an alkaline solution. Liquid potash fertilizer is used.

The invention provides a new solution method and approach for the follow-up treatment of straws produced by phytoremediation of soil heavy metal pollution, enables efficient and sustainable development of phytoremediation technology, and also provides a new approach for plant resource utilization.

Detailed ways

Example 1:

1) cleaning the tobacco straw after the phytoremediation of the soil heavy metal pollution in the mature stage after harvesting, and drying it in an oven at 60 degrees;

2) Weigh the dried tobacco straw and pulverize it with a pulverizer and weigh 10 g and place it in a clean quartz boat, then place it in a tube furnace fed with high-purity nitrogen for firing, and the temperature is set to 300-350 ° C, The time is set to 2 hours, and the absorption liquid is 0.1 mol/L nitric acid to obtain biochar;

3) After the completion of step 2), weigh the fired biochar to measure its yield, then weigh 10 g of the fired biochar and put it into a clean beaker, add 300 ml of clean water, and adjust its pH with nitric acid. When the value is 1, stir for 3 hours to extract heavy metals, and then rinse the residual acid in the biochar with clean water for filtration or centrifugal dehydration;

4) Centrally collect the solution extracted in step 3), and adjust the pH value to 9-11 with potassium hydroxide or potassium carbonate solution, so that the heavy metals are precipitated, and after the heavy metals are recovered by separation and filtration, a high-potassium-containing liquid fertilizer is obtained.

The following experiments prove that the changes of heavy metals and nutrient elements in the process of preparing biochar obtained in the examples of the present invention, and in the process of separating heavy metals, the content of heavy metals is reduced, and the K element is increased.

Experiment 1: Take 10g of dried tobacco straw and put it into a tube furnace and pass it into nitrogen for firing. The firing time is 2 hours. After cooling at the same temperature, take it out for digestion and on-machine testing. The test results are shown in Table 1.

Table 1: Changes of heavy metals and nutrients in tobacco straws fired at 300 and 350℃

Through the experiment, it was found that the heavy metals in the tobacco straw began to volatilize significantly at 400 °C, and the cadmium was completely volatilized at 600 °C. At ℃, the volatilization of cadmium is small, and the yield of biochar is also relatively high, and the changes of other nutrients are not very large, so the subsequent extraction experiments choose to burn biochar at 300 ℃.

Experiment 2: Weigh 10g of biochar fired at 300°C into a beaker, add 300ml of clean water, place it on a magnetic stirrer and stir for 20 minutes, stir well, adjust the pH to 1 with nitric acid, and filter after stirring for 3h , collect the filtrate in a beaker, stir, adjust the pH to 9, 10, and 11 points with potassium hydroxide or potassium carbonate solution, stir well, take 5ml of solution at each point and filter for on-machine detection; The results are shown in Table II.

Table 2: Changes of heavy metals and nutrients in biochar at 350℃ at different pH (unit: ug; "/" means not detected)

It can be seen from Table 2 that when the pH is adjusted to alkaline, the total amount of elements in the solution decreases, and the heavy metal elements Pb, Zn, Cu, and Cd cannot be detected when the pH is 9, indicating that under alkaline conditions, heavy metals undergo chemical reactions. The reaction resulted in a precipitation, and the total amount of potassium increased due to the addition of potassium hydroxide or potassium carbonate solution during pH adjustment.

Claims (1)

1. A resource utilization method of high-potassium-content straws produced after heavy metal pollution of soil remediation by plants is characterized by comprising the following steps:

1) harvesting tobacco straws, oil sunflower straws, sesame straws or peanut straws after the heavy metal pollution of the plant restoration soil in the mature period, cleaning and drying;

2) weighing dried straws, crushing the straws by using a crusher, placing the crushed straws in a tubular furnace into which high-purity nitrogen is introduced, and firing the straws at a low temperature, wherein the temperature is set to be within the range of 300-350 ℃, the time is set to be 2 hours, and the absorption liquid is 0.1mol/L nitric acid to obtain biochar;

3) after the step 2), putting the fired biochar in clean water, regulating the pH value of the biochar to be 1-3 by using nitric acid, stirring for 3 hours, dissolving out heavy metals, and washing residual acid in the biochar by using clean water for filtering or a centrifugal dehydration mode;

4) collecting the solution extracted in the step 3) in a centralized manner, regulating the pH value to 9-11 by using a potassium hydroxide or potassium carbonate solution to precipitate heavy metals, separating, filtering and recovering the heavy metals to obtain the liquid fertilizer containing high potassium.